A method for the powder pack coating of metal objects has been disclosed in German Patent Publication DE 2,560,523. The known method has the disadvantage that it is not suitable for coating internal surfaces inside hollow components, because the metal components to be coated are embedded in a powder packing of donor metal powder enclosing the outside of the components, whereby any connecting ducts between external and internal surfaces are disadvantageously clogged with powder. A uniform internal coating is not ensured, because there is no donor metal in the component's cavities that, after the powder pack coating has been completed, can be removed from the cavities without leaving residues behind. These residues result in a nonuniform coating on the internal surfaces.
To avoid the above problem, gas diffusion coating has been used, as disclosed in EP 0,349,420, for use on hollow components. Solid powder particles do not come into contact with the component where gas diffusion coatings are applied. However, gas diffusion coating methods have the disadvantage that conventional simple powder pack coating devices can no longer be used in mass production operations, so that these coating devices must be replaced by substantially more complex coating systems. Even conventional powder compositions of the donor metal and the heat treatments for the coating process can no longer be used where hollow components of complicated configurations are to be coated on the inside. Additionally, the donor metal gas will deplete on its passage through the cavities of the component being coated, so that the coating thickness disadvantageously becomes dependent upon the length of the flow path of the donor gas through the component.